title: Effect of CO₂ on the ventilatory sensitivity to rising body temperature during exercise.
abstract: We examined the degree to which ventilatory sensitivity to rising body temperature (the slope of the regression line relating ventilation and body temperature) is altered by restoration of arterial PCO(2) to the eucapnic level during prolonged exercise in the heat. Thirteen subjects exercised for ~60 min on a cycle ergometer at 50% of peak O(2) uptake with and without inhalation of CO(2)-enriched air. Subjects began breathing CO(2)-enriched air at the point that end-tidal Pco(2) started to decline. Esophageal temperature (T(es)), minute ventilation (V(E)), tidal volume (V(T)), respiratory frequency (f(R)), respiratory gases, middle cerebral artery blood velocity, and arterial blood pressure were recorded continuously. When V(E), V(T), f(R), and ventilatory equivalents for O(2) uptake (V(E)/VO(2)) and CO(2) output (V(E)/VCO(2)) were plotted against changes in T(es) from the start of the CO(2)-enriched air inhalation (ΔT(es)), the slopes of the regression lines relating V(E), V(T), V(E)/VO(2), and V(E)/VCO(2) to ΔT(es) (ventilatory sensitivity to rising body temperature) were significantly greater when subjects breathed CO(2)-enriched air than when they breathed room air (V(E): 19.8 ± 10.3 vs. 8.9 ± 6.7 l·min(-1)·°C(-1), V(T): 18 ± 120 vs. -81 ± 92 ml/°C; V(E)/VO(2): 7.4 ± 5.5 vs. 2.6 ± 2.3 units/°C, and V(E)/VCO(2): 7.6 ± 6.6 vs. 3.4 ± 2.8 units/°C). The increase in Ve was accompanied by increases in V(T) and f(R). These results suggest that restoration of arterial PCO(2) to nearly eucapnic levels increases ventilatory sensitivity to rising body temperature by around threefold.
authors.affiliation: Institute of Health and Sports Science, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Hayashi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Honda
authors.forename: Natsuki
authors.initials: N
authors.lastname: Miyakawa
authors.forename: Naoto
authors.initials: N
authors.lastname: Fujii
authors.forename: Masashi
authors.initials: M
authors.lastname: Ichinose
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Koga
authors.forename: Narihiko
authors.initials: N
authors.lastname: Kondo
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishiyasu
mesh_terms: D000280:Administration, Inhalation; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology*; D002245:Carbon Dioxide / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D005082:Physical Exertion / Q000187:drug effects / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D015656:Respiratory Mechanics / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide